Align ArrayWindows trait impls with Windows

[cuviper]

With slice::ArrayWindows getting ready to stabilize in 1.94, I noticed that it currently has some differences in trait implementations compared to slice::Windows, and I think we should align these.

• Remove derive(Copy) -- we generally don't want Copy for iterators at all, as this is seen as a footgun (e.g. remove Copy impls from remaining iterators #21809). This is obviously a breaking change though, so we should only remove this if we also backport the removal before it's stable. Otherwise, it should at least be replaced by a manual impl without requiring T: Copy.
• Manually impl Clone, simply to avoid requiring T: Clone.
• impl FusedIterator, because it is trivially so. The since = "1.94.0" assumes we'll backport this, otherwise we should change that to the "current" placeholder.
• impl TrustedLen, because we can trust our implementation.
• impl TrustedRandomAccess, because the required __iterator_get_unchecked method is straightforward.

r? libs-api

@rustbot label beta-nominated
(at least for the Copy removal, but we could be more selective about the rest).

[hkBst]

The minimal fix would seem to be to backport an unstabling PR, then let these changes ride the train as normal.

[cuviper]

@hkBst "unstabling" is an option, but that comes with a lot of secondary effects, like needing to reverse the bootstrap-feature change in commit 3dc7a1f.

Backporting just the Copy removal would be simplest action. The rest can ride the train, no problem.

[hkBst]

Given the number of missed things, it seems clear that this feature did not receive enough attention before it was stabilized. That's why I think unstabilizing is the most principled solution. Beta is the least used/tested release channel so backporting like this feels awfully close to committing straight to stable ;P. These changes seem straightforward enough, but the changes that end up causing problems often seem so as well...